Yes I can believe the prices. the new trucks are so expensive that older cab chassis 4x4 get way above market value. I think that 12K is steep. I bought an 86 k-35 GMC in 1994 for 8200.00, kept it four years and sold it for 9200.00 when I bought my new one. It to had the gas engine with 60K on the meter. I would actually prefer the gas to a diesel in that year truck. It will last just as long and be alot more reliable. When I sold the truck the drivetrain and cab were mint. the flat bed in the rear needed to be replaced. the new owner added one for a grand, so he was into the truck for about 10K when he was done.
You just cant kill them, but I like the ride of my newer truck alot better.
I am not the biggest and I am not the best but I fall somewhere comfortably in between.